The present invention relates to a device and method for resource management in mesh communication systems, more particularly but not exclusively to mesh connected systems which include a satellite element, and to terrestrial wireless communication systems.
Satellite Communication Systems
Almost all the existing satellite communication systems are based on the transponder principle of operation. Almost all the existing transponders are located on geostationary satellites. A transponder receives the signals transmitted from the ground (uplink) and filters those in the frequency band of operation, amplifies them and retransmits (downlink) in a frequency band different from the uplink band. The transmissions that pass the transponders are usually formatted according to international standards and limitations. The most popular standard today is DVB-S for transmission of digital television broadcasting. The new standard DVB-S2 is gradually taking the place of the DVB-S in new systems as well as in replacement of existing systems.
In the typical star type of system, a central station called the hub, controls the network. The DVB-S/S2 method is used for the outbound link or forward link (from the hub to the terminals) and the inbound link or return link (from the terminals to the hub) uses the DVB-RCS standard.
For example in the Amos 2 satellite there are 11 operating transponders in the Ku band, each having a bandwidth of 72 MHz. For example, one of them has an uplink frequency band of 13040.5±36 MHz and a downlink frequency band of 10740.5±36 MHz. The YES broadcasting company uses such a transponder with two DVB-S signals each one 36 MHz wide.
Resource Management
For the usage of a transponder or part thereof, the operator of the satellite communication system has to pay to satellite owner according to the bandwidth and the downlink power he is allowed to use. These resources are shared among the active transmissions. Therefore in order to save operating costs, the satellite communication system has to control the transmissions and to share the frequency band according to the requirements of the users.
For a star type of system that has a central hub that communicates with user terminals, control is carried out by the control center in the hub according to users needs. For other types of systems that are not of star type, like point to point systems, control is carried out by a dedicated communication and control system that operates in addition to point to point links.
Types of Communication Systems
According to the different types of links among the users in the network it is possible to define several systems:                a. Star where all users are connected by bidirectional or directional links to a hub        b. Point to point where two users are connected by bidirectional or directional link        c. Multiple point to point where pairs of users are connected by bidirectional or directional links        d. Mesh where users are connected by bidirectional or directional links        e. Fully Mesh where all users are connected to all other users by bidirectional links.        
Connectivity
User A is connected to user B if a message can be transmitted from A to B directly or via other users' terminals. The minimal number of transmissions required for transmitting from A to B is the length of the connection. The smallest length is one (one hop). A fully connected system is a system where each user is connected to any other user with a connection of any length. The connectivity of the system is then to the largest length of connection among any two users. The connectivity is the diameter of graph theory. For example:
(a) A star system with bidirectional links has a connectivity of two.
(b) A fully mesh system has a connectivity one.
(c) N pairs Ai Bi i=1, . . . , N connected by bidirectional links can be transformed to a connected system if we add single links between Ai Bi+1 i=1, . . . , N−1 and between AN and B1. The connectivity of the resulting system is 2N−1.
(d) N pairs Ai Bi i=1, . . . , N connected by bidirectional links can be transformed to a connected system if we add single links between Ai Ai+1 i=1, . . . , N−1 and between AN and A1. The connectivity of the resulting system is N.
Synchronization Methods
There are several methods of synchronization. Some of the methods include:                synchronization based on GPS signals        Distribution from one terminal, ‘clock master’, to all the others, via special timing packets. The delays among stations may be known.        Distribution from several terminals. Each terminal has a time and an accuracy figure. The receiving terminal may adjust its timing and accuracy figure according to a combination of its existing timing and accuracy figure, and the received timing and accuracy figure.        
Network Clock Reference
As an example, in a star system based on DVB-S/S2 for the outbound link and using DVB-RCS for the inbound link, time synchronization is a must. All system timing is maintained through a global clock distributed on the forward link. A timestamp of the 27 MHz Network Clock Reference (NCR) is recovered by each RCST so that an RCST has an absolute time reference, which would be in addition to a frequency reference. The return link framing structure is built on the NCR. This includes the start of bursts that are referenced to the NCR count and guard bands that are defined as offsets to the burst start in terms of NCR ticks. The entire return link structure is transmitted as a table on the forward link that defines the framing, coding, preambles and slots.
Another possible algorithm for synchronization is IEEE 1588 2008.
As mentioned, in the case of the star connection, resource allocation is based on a central hub, to which all terminals are directly linked. A problem arises however with the mesh type networks, where there is no central entity connected at a single hop to all terminals. How is resource allocation to be efficiently and dynamically managed?